1. Field of the Invention
The present invention relates to a lens barrel.
2. Description of the Related Art
Small-sized lens barrels which incorporate a lens drive mechanism including a stationary barrel, a gear/helicoid ring and a drive pinion, wherein a male helicoid formed on a gear/helicoid rib (annular rib) projecting radially outwards from a rear end of the gear/helicoid ring is engaged with a female helicoid formed on an inner peripheral surface of the stationary barrel and wherein the drive pinion that rotates at a fixed position is engaged with a spur gear formed on the thread of the male helicoid of the gear/helicoid ring, are known in the art. A linear guide ring which is linearly guided along an optical axis is disposed around the gear/helicoid. The gear/helicoid ring is provided immediately in front of the gear/helicoid rib with a plurality of bayonet lugs, while the linear guide ring is provided on an inner peripheral surface thereof with a circumferential groove in which the plurality of bayonet lugs of the gear/helicoid ring are engaged so that the gear/helicoid ring and the linear guide ring move together in the optical axis direction while allowing the gear/helicoid ring to rotate freely relative to the linear guide ring. Rotation of the gear/helicoid ring by rotation of the drive pinion causes one or more focal-length varying lens groups, which are linearly guided along the optical axis via the linear guide ring, to move along the optical axis to perform a zooming operation.
In such lens barrels, the axial length of the gear/helicoid rib is to be as short as possible to reduce the length of the lens barrel to the extreme. However, if the axial length of the gear/helicoid rib is excessively short, a sufficient length of engagement between the spur gear of the gear/helicoid ring and the drive pinion in the optical axis direction cannot be secured, which makes it impossible to perform a lens driving operation with stability.